1. Technical Field
The present invention relates to an AC (alternating current) motor mounted on automobiles, trucks, and others and a control apparatus for the AC motor, and in particular to, an AC motor known as a reluctance motor and a control apparatus for the control apparatus.
2. Related Art
Conventionally, as exemplified in a patent reference 1: Japanese Patent Laid-open publication 2009-273216, three-phase AC motors are widely used. Additionally, in a patent reference 2: Japanese Patent No. 40414343, there is shown an AC motor driven on multi-phase AC currents and produced to have ring-shape windings.
FIG. 43 shows an example from the patent reference 1, which shows a longitudinal section outlining the configuration of a three-phase AC motor. This three-phase AC motor is provided with a stator ST and a rotor RT. The rotor RT has a motor output shaft 431, a rotor core 432, and N-pole permanent magnets 437 and S-pole permanent magnets 438 which are attached on a rotor surface. The motor output shaft 431 is rotatably supported by bearings 433 of the stator ST. The stator ST has a motor case 436 and a stator core 434 with windings. A reference 435 shows coil ends of the windings.
FIG. 44 is a cross section laterally cut along a section AA-AA in FIG. 43. The motor is a motor of AC three-phase, bipoles and 6-slot type. The windings are wound in a full-pitch and concentrated winding manner. The stator has teeth 441, 442, 443, 444, 445 and 446 arranged in a circumferential direction CR.
Respective slots, each being between mutually adjacent teeth, allow three-phase windings to be wound therethrough, in which a U-phase winding is wound to be routed as shown by a winding from a reference 447 to a reference 44A, a V-phase winding is wound to be routed as shown by a winding from a reference 449 to a reference 44C, and a W-phase winding is wound to be routed as shown by a winding from a reference 44B to a reference 448. The respective windings are wound at an electrical angle of 180 degrees.
Though FIGS. 43 and 44 exemplify bipolar motors, this type of motor is frequently used as multiple motors having four or more poles. In addition, through the examples show the concentrated winding with which the winding for each phase is wound through one slot, full-pitch winding motors commonly adopt a distributed winding manner with which the winding for each phase is distributed into two or more slots.
FIG. 45 shows a configuration for driving the foregoing three-phase AC motors with the use of a three-phase AC inverter. A reference 45E shows a U-phase winding to allow U-phase current Iu to pass therethrough. A reference 45F shows a V-phase winding to allow V-phase current Iv to pass therethrough. A reference 45G shows a W-phase winding to allow W-phase current Iw to pass therethrough. A reference 2E shows a DC voltage source which is composed of a battery, for instance, references 51, 452, 453, 454, 455 and 456 show power transistors, and references 457, 458, 459, 45A, 45B, 45C show diodes arranged parallely with the respective power transistors. The transistors can be a variety of power semiconductor devices including IGBTs and FETs.
FIG. 46 shows the configuration of a three-phase AC motor in which the permanent magnet type of rotor using the permanent magnets 437 and 438 shown in FIG. 44 is replaced by a reluctance rotor 461 using a soft magnetic member. A reference 463 indicates a space, thereby producing a larger magnetic resistance. This drives the reluctance motor to generate torque depending on a difference in degrees of the magnetic resistance.
A three-phase AC inverter shown in FIG. 45 is used to cause torque to be generated in the counterclockwise direction CCW. If the rotor currently presents a rotation position shown in FIG. 46, the inverter is used to make a positive current Iu pass though the U-phase windings 447 and 44A and make a negative current Iv pass through the V-phase windings 449 and 44C. When current passing through the W-phase windings 44B and 448 becomes zero, a magnetomotive force is generated in a direction shown by a dotted arrow 462.
A magnetomotive force generated in the direction passing through the teeth 441 and 444 of the stator, which are stator poles, becomes zero, because magnetomotive forces on the U-phase current Iu and the V-phase current Iv are canceled out due to their mutually opposite directions. Thus, in FIG. 46, magnetomotive forces are generated in directions from the teeth 445 and 446 to the teeth 442, 443 respectively, so that a magnetic flux 464 mainly passes from the tooth 445 to the 442. An attraction force generated between the teeth of the stator and the rotor 461 generates a torque in the counterclockwise direction CCW, which is shown by an arrow 465.
In synchronization with the rotation of the rotor 461, three-phase AC currents are supplied in turn to the respective phase windings to rotate the direction of the magnetomotive force 462. This enables the reluctance motor shown in FIG. 46 to rotate continuously.
The reluctance motor shown in FIG. 46 does not use permanent magnets which are expensive, allowing this motor to be produced at relatively less cost. However, the inverter shown in FIG. 45 needs 6 power transistors to drive one motor, resulting in a drawback of increasing production cost. It is thus desired to raise, as a set, competitiveness of the motor and the inverter in terms of their performances, sizes, and production cost.
The stators shown in FIGS. 44 and 46 employ the full pitch winding, thus making the motors larger in size owing to the coil end portions of the respective phase windings overlapped on one another.
Additionally the motor shown by the patent reference 2, which is driven by multi-phase AC currents, needs an inverter provided with which many power transistors, raising production cost thereof.